Catalyst systems for polycondensation reactions

ABSTRACT

The invention pertains to new catalyst systems for polycondensation reactions, for example for producing polyethylene terephthalate. In accordance with the invention, complex compounds with hydrotalcite-analogous structures of general formula [M(II) 1−x M(III) x (OH) 2 ] x+ (A n−   x/n ).mH 2 O are used, wherein M(II) represents divalent metals, preferably Mg or Zn or NI or Cu or Fe(II) or Co, and M(III) represents trivalent metals, for example Al or Fe(III), and A represents anions, preferably carbonates or borates. These catalysts can be calcinated and can be used in combination with phosphorus compounds that contain at least one hydrolyzable phosphorus-oxygen bond.

[0001] The invention pertains to new catalyst systems for polycondensation reactions.

[0002] The synthesis of polyesters, for example polyethylene terephthalate, requires the use of catalysts in the polycondensation step. The literature contains an abundance of patents describing the use of various catalytically active substances. Today especially antimony and titanium compounds are used on a large industrial scale in the manufacturing of polyethylene terephthalate. This is also reflected in the large number of patents that describe the use of such compounds. Polyester-soluble antimony compounds are described in U.S. Pat. Nos. 3,965,071; 3,998,793; 4,039,515; 4,116,942; 4,133,800; 4,454,312; 5,750,635; and 5,780,575 as polycondensation catalysts. Modified antimony derivatives (stabilization by substances with double bonds to prevent reduction to metallic antimony) are, for example, subjects of patents U.S. Pat. No. 4,067,856; U.S. Pat. No. 4,067,857; and U.S. Pat. No. 4,130,552. Antimony salts of trimellitic acid esters are likewise used as catalysts in the manufacturing of polyethylene terephthalate (U.S. Pat. No. 5,478,796). Titanium derivatives, especially tetraalkyl titanates, are protected in the patents U.S. Pat. No. 4,039,515; U.S. Pat. No. 4,131,601; U.S. Pat. No. 4,482,700; U.S. Pat. No. 5,066,766; U.S. Pat. No. 5,302,690; WO 97/45470; and U.S. Pat. No. 5,744,571. A combination of sulfonic acid, titanate and antimony (or germanium) compound is the subject of U.S. Pat. No. 5,905,136. Germanium compounds are also described as catalysts for the polycondensation reaction (U.S. Pat. No. 5,378,796; U.S. Pat. No. 5,830,981; U.S. Pat. No. 5,837,786; and U.S. Pat. No. 5,837,800). Catalytically active compounds in a polycondensation reaction are likewise borates and acetates of zinc, calcium, cobalt, lead, cadmium, lithium, or sodium (U.S. Pat. No. 4,115,371).

[0003] Defined silicon compounds (2-cyanoethyltriethoxysilane and 3-aminopropyltriethoxysilane) are protected in a US patent (U.S. Pat. No. 4,077,944) as polycondensation catalysts.

[0004] The combination of several metal compounds is described in the following patents: U.S. Pat. No. 4,080,317 (Sb/Pb/Zn, Sb/Pb/Ca, Sb/Zn, Sb/Pb/Mg, Sb/Pb/Ca/Mn, Sb/Pb/Ca/Zn, Sb/Pb/Li, Sb/Mn, Ti/Ca, Ge/Ga, Ge/Zn, and Ge/K); U.S. Pat. No. 4,104,263 (Sb(Zr)/Zn(Ca,Mn)); U.S. Pat. No. 4,122,107 (Sb/Zn(Ca,Mn)); U.S. Pat. No. 4,356,299, U.S. Pat. No. 4,501,878, and U.S. Pat. No. 5,286,836 (Ti/Sb); U.S. Pat. No. 4,361,694 (Ti/Si); U.S. Pat. No. 4,468,489 (Ti,Zr,Ge,Zn); U.S. Pat. No. 4,499,226 and U.S. Pat. No. 5,019,640 (Sb/Co); U.S. Pat. No. 5,008,230 (Co(Zn)/Zn(Mn,Mg,Ca)/Sb); U.S. Pat. No. 5,138,024 and U.S. Pat. No. 5,340,909 (Zn/Sb); U.S. Pat. No. 5,565,545 and U.S. Pat. No. 5,644,019 (Sb/Ge); U.S. Pat. No. 5,596,069 (Co/Al); U.S. Pat. No. 5,608,032 and U.S. Pat. No. 5,623,047 (Sb/Co(Mg,Zn,Mn,Pb)); U.S. Pat. No. 5,656,221 (Sb/Co/Mn); U.S. Pat. No. 5,714,570 (Sb/Ti/Zn); and U.S. Pat. No. 5,902,873 (Ti(Zr)/lanthamide). At least one constituent of these complex catalysts is a “classical” polycondensation catalyst, either antimony, titanium, or germanium.

[0005] Finely dispersed titanates are the subject of U.S. Pat. No. 5,656,716. Jointly precipitated titanium and silicon compounds and titanium and zirconium compounds are described in U.S. Pat. Nos. 5,684,116 and 5,789,528.

[0006] A polycondensation catalyst on the basis of zeolites (alkali or alkaline earth metal-modified aluminosilicate) is protected in U.S. Pat. No. 5,733,969. The use of titanium compounds leads to yellowing of the polyester produced during polycondensation and processing. Especially during the use of polyethylene terephthalate as a food packaging, this color is undesirable.

[0007] The use of antimony as a catalyst is permitted only within precisely established boundaries, since this substance, as a heavy metal, is physiologically problematic.

[0008] The goal of this invention is to discover a catalyst system for the polycondensation, especially of polyethylene terephthalate, polybutylene terephthalate, or polytrimethylene terephthalate, which is physiologically safe and makes it possible to use the polycondensation products for food packaging. In terms of catalytic activity in polycondensation and selectivity, it must be compatible with conventional catalysts and must not influence the processing properties of polyester at all or only to the desired degree.

[0009] Quite surprisingly, it was found that complex compounds with hydrotalcite-analogous structures of the general formula [M(II)_(1−x)M(III)_(x)(OH)₂]^(x+)(A^(n−) _(x/n)).mH₂O, (the use of which was previously described only as a filler (U.S. Pat. No. 5,362,457; U.S. Pat. No. 5,225,115; JP 09 077,962; JP 02 308,848; JP 61 118,457; JP 56 059,864), in olefin isomerizations, as an adsorbents (halogen trapper), as a carrier material for catalysts, flame retardant, molecular sieve, anion exchanger and catalyst for alcohol reactions (isophorone synthesis), hydrogenations, polymerizations, and reforming reactions (F. Cavani, F. Trifiro, A. Vaccari, Catalysis Today 11 (1991), 173-301)), before or after calcination, alone or in combination with phosphorus compounds that contain at least one hydrolyzable phosphorus-oxygen compound, are excellently suited for catalysis of polycondensation reactions, especially for the production of polyalkylene terephthalate.

[0010] In the formula mentioned, M(II) represents divalent metals, preferably Mg or Zn or Ni or Cu or Fe(II) or Co, and M(III) represents trivalent metals, preferably Al and Fe, and A represents anions, preferably carbonates or borates or titanyl compounds.

[0011] The particle size of the hydrotalcite used falls in the range of 0.1 to 50 μn, preferably 0.5 to 5 μn.

[0012] The calcination of the hydrotalcites can be performed at temperatures of 200° C. to 800° C., preferably at 400° C. to 650° C.

[0013] As phosphorus compounds which contain at least one hydrolyzable phosphorus-oxygen bond, phosphoric acid esters or esters of phosphorous acid can be used.

[0014] The catalyst system in accordance with the invention is used in the concentration ratio of hydrotalcite to phosphorus compound of 1:0.5 to 1:4, preferably 1:1 to 1:2.

[0015] The untreated or the calcinated hydrotalcite-analogous derivatives in combination with phosphorus compounds as stabilizers with at least one hydrolyzable phosphorus-oxygen bond show increased catalytic activity and selectivity in comparison to conventional catalysts and are characterized by high food compatibility.

[0016] It has been found that these substances, made up of several components, are highly catalytically selective, relatively independent of their composition, although the individual constituents catalyze polycondensation reactions either not at all or only with a very low selectivity and thus generate a high fraction of byproducts. It was also found that with the targeted selection of the constituents, surprisingly it was possible to influence the applications properties of the polyesters, for example the crystallization behavior. The polycondensation with the catalyst system in accordance with the invention is carried out under vacuum in a liquid phase at temperatures of 230° C. to 280° C. or in a solid phase at temperatures of 170 to 240° C.

[0017] The addition of phosphorus compounds with at least one hydrolyzable phosphorus-oxygen bond leads to improved thermal stability of the polyesters, especially in the industrially required long residence times of the liquid polyesters under normal pressure in comparison to polyesters produced with conventional [catalysts], for example with catalysts on the basis of antimony and titanium compounds, but also in comparison to products produced under hydrotalcite catalysis.

[0018] Through the combination of hydrotalcite-analogous compound/stabilizer, molecular weight degradation and discoloration of the polyester can be lowered significantly without a negative influence on other important processing properties of the polyester, for example the crystallization behavior and the clarity of the final product.

[0019] In the following, the invention will be explained on the basis of exemplified embodiments.

[0020] In a 250-ml, single-necked flask with agitator and distillation attachment, 100 g precondensate of terephthalic acid and ethylene glycol with an average molecular weight was placed together with the catalyst. This apparatus was evacuated to about 0.5 mbar and purged with nitrogen. This process was repeated a total of three times. The glass flask was dipped into a hot salt bath at 280° C. and the precondensate allowed to melt at this temperature. As soon as the melting was complete, vacuum was carefully applied.

[0021] Following termination of the polycondensation by purging with nitrogen, the product was allowed to cool in the flask, and the polyester was characterized according to its separation from the adhering glass.

[0022] The intrinsic viscosity (IV) was determined on an apparatus from the Schott Company (AVSPro) of 250 mg resin dissolved in 50 ml phenol/dichlorobenzene (1:1).

[0023] DSC measurements were performed on a Perkin-Elmer DSC 7.

[0024] The acetaldehyde determination took place according to the following procedure:

[0025] The PET material was precooled in liquid nitrogen and ground in an ultracentrifuge mill. The ground material was immediately weighed into a headspace vial and closed gas-tight with a septum. After holding a constant quantity of gas at 150° C. for 90 minutes in the headspace sampler, the gas was injected onto the GC column, at a defined pressure. The color numbers were determined with a LUCI 100 spectrophotometer from the Lange Company.

[0026] Table 1 contains characteristic values of polyesters that were obtained by polycondensation reactions at temperatures of 280° C. using various hydrotalcite catalysts. TABLE 1 Characterization of polyethylene terephthalate from polycondensation reactions with various untreated or calcinated hydrotalcite-analogous derivatives Reaction Concentration time Acetaldehyde Tg¹ Tc² Tcc³ Tm⁴ Experiment no. Catalyst (ppm) (minutes) IV (dl/g) (ppm) (° C.) (° C.) (° C.) (° C.) 1 (comparison Antimony (III) acetate 350 180 0.7480 14.2 79.7 198.9 163.2 248.6 example) 2 (example in Al-Mg-hydrotalcite (acc. 100 180 0.5648 14.4 78.9 197.1 143.5 254.3 acc. with the to U.S. Pat. No. 5,437,720); invention) calcinated (18 hours, 450° C.) 3 (example in Al-Mg-hydrotalcite (acc. 250 165 0.7350 20.7 81.5 184 153.5 251.7 acc. with the to U.S. Pat. No. 5,437,720); invention) calcinated (18 hours, 450° C.) 4 (example in Al-Mg-hydrotalcite (acc. 500 150 0.6862 16.7 80.9 183.2 150.8 250.1 acc. with the to U.S. Pat. No. 5,437,720); invention) calcinated (18 hours, 450° C.) 5 (example in Al-Mg-hydrotalcite (acc. 1000 150 0.8412 17.4 82.5 179.3 154.2 252.9 acc. with the to U.S. Pat. No. 5,437,720); invention) calcinated (18 hours, 450° C.) 6 (example in Al-Mg-hydrotalcite (acc. 1000 90 0.8893 44 84.1 175.2 153.5 252.3 acc. with the to U.S. Pat. No. 5,437,720) invention) 7 (example in Zn₆Al₂(OH)₁₆CO₃*H₂O 500 180 0.6932 16.4 81.9 185.3 152.8 254.4 acc. with the calcinated (18 hours, invention) 450° C.) 8*(example in Mg₄Al₂(OH)₁₂(B₃O₃(OH)₄)₂* 500 210 0.6617 22.2 85.2 207.2 251.6 acc. with the H₂O calcinated invention) (18 hours, 450° C.) 9*(example in Mg₄Al₂(OH)₁₂(B₃O₃(OH)₄)₂* 1000 150 0.7704 19.7 79.3 198.4 144 249.6 acc. with the H₂O calcinated invention) (18 hours, 450° C.) 10*(example Mg₃ZnAl₂(OH)₁₂ 1000 165 0.6302 17.3 79.6 189.4 153.5 254.3 in acc. with (B₃O₃(OH)₄)₂* the invention) H₂O calcinated (18 hours, 450° C.) 11*(example Mg₂Zn₂Al₂(OH)₁₂ 1000 180 0.7031 17.3 82.5 201.8 136.1 251.6 in acc. with (B₃O₃(OH)₄)₂* the invention) H₂O calcinated (18 hours, 450° C.) 12*(example MgZn₃Al₂(OH)₁₂ 1000 120 0.7608 20.2 84.3 201.1 138.1 255.1 in acc. with (B₃O₃(OH)₄)₂* the invention) H₂O calcinated (18 hours, 450° C.) 13*(example Zn₄Al₂(OH)₁₂(B₃O₃(OH)₄)₂* 1000 135 0.8362 22.8 83.3 200.8 137.4 251.7 in acc. with H₂O calcinated the invention (18 hours, 450° C.)

[0027] Table 1 clearly shows that all tested untreated or calcinated hydrotalcite-analogous derivatives have catalytic activity. The synthesized polyethylene terephthalate, depending on the catalyst used, has different processing-related properties.

[0028] An additional important criterion for assessing the suitability of untreated or calcinated hydrotalcite-analogous derivatives is their catalytic activity in so-called solid state polymerization (SSP).

[0029] For these experiments, six of the polyesters listed in Table 1 were subjected to SSP. For this purpose the products were left for 96 hours at 200° C. in a vacuum drying oven. After cooling, characteristic values relevant for applications technology were determined.

[0030] The results of solid state polymerizations of polyethylene terephthalate are summarized in Table 2. TABLE 2 Polyesters from solid state polymerization Concentration IV (dl/g) after IV (dl/g) Acetaldehyde Tg Tc Tcc Tm No. Catalyst (ppm) polycondensation after SSP (ppm) (° C.) (° C.) (° C.) (° C.) 1 Zn₆Al₂(OH)₁₆CO₃*H₂O 500 0.6932 1.1891 0.3 84.1 162.8 166.9 249.6 calcinated (18 hours, 450° C.) 2 Al-Mg-hydrotalcite 100 0.5648 0.7755 0.4 82.2 178.6 156.1 253 (acc. to U.S. Pat. No. 5,437,720); calcinated (18 hours, 450° C.) 3 Al-Mg-hydrotalcite 250 0.7350 0.9549 0.4 83.9 172.9 161.5 253 (acc. to U.S. Pat. No. 5,437,720); calcinated (18 hours, 450° C.) 4 Al-Mg-hydrotalcite 500 0.6862 1.0775 0.3 83.1 166.2 161.5 249.6 (acc. to U.S. Pat. No. 5,437,720); calcinated (18 hours, 450° C.) 5 Al-Mg-hydrotalcite 1000 0.8412 1.1005 0.3 84.4 170.9 162.8 252.3 (acc. to U.S. Pat. No. 5,437,720); calcinated (18 hours, 450° C.) 6 Al-Mg-hydrotalcite 1000 0.8893 1.301 0.9 84.6 176.7 155.5 253.2 (acc. to U.S. Pat. No. 5,437,720) 7 Mg₄Al₂(OH)₁₂(B₃O₃(OH)₄)₂*H₂O 500 0.6617 0.8509 0.6 83.5 201.4 140.8 253.0 calcinated (18 hours, 450° C.) 8 Mg₃Al₂(OH)₁₂(B₃O₃(OH)₄)₂*H₂O 1000 0.6302 0.8009 0.6 82.7 179.2 161.5 254.4 calcinated (18 hours, 450° C.)

[0031] Table 2 shows the fundamental suitability of the untreated or calcinated hydrotalcite-analogous derivatives as catalysts for polycondensation reactions in both liquid and solid phase.

[0032] It is especially important that it is possible by selecting the constituents of these complex catalysts to systematically influence the process technology properties of the polyester resins, for example the crystallization behavior.

[0033] The use of the hydrotalcite catalysts in accordance with the invention in combination with phosphorous compounds which contain at least one hydrolyzable phosphorus-oxygen bond is described in the examples that follow.

EXAMPLE 14 (COMPARISON EXAMPLE)

[0034] In a 200 liter reactor of alloyed steel, a suspension of 60.675 kg terephthalic acid and 1.44 kg isophthalic acid were placed in 31.6 kg ethylene glycol. Under agitation, this reaction mixture was treated with 45.5 g antimony triacetate and 8.125 g cobalt acetate tetrahydrate in 1000 g ethylene glycol, and 34.65 g tetramethylammonium hydroxide in 500 g ethylene glycol. The closed reactor was heated to 272° C. At 2.8 bar the slow expansion of the pressurized container was started. After about 20 minutes under normal pressure, 12 g phosphoric acid in 500 g ethylene glycol were added. Then the liquid phase polymerization was started by slow application of the vacuum. After about 60 minutes the final vacuum of about 4 mbar was reached. The end of the reaction was shown by the attainment of a defined rotary momentum. The reaction vessel was relaxed with nitrogen, and the reactor emptied through several nozzles over a period of about 60 minutes into a water bath. The product strands were immediately granulated.

[0035] The molecular weight and the color of various product batches were determined.

[0036] Table 3 gives a survey of the values determined.

EXAMPLE 15 (COMPARISON EXAMPLE)

[0037] In an apparatus in analogy to Example 14, the same amount of terephthalic and isophthalic acid as well as ethylene glycol, tetramethylammonium hydroxide, and cobalt acetate tetrahydrate were placed as in Example 14. After the esterification was complete, under a slight vacuum 20 g Pural (hydrotalcite with about 60 percent magnesium) were added. The addition of phosphoric acid was not performed. The liquid phase polycondensation was performed and ended in the manner described in Example 14.

EXAMPLE 16 (EXEMPLIFIED EMBODIMENT)

[0038] In an apparatus analogous to Example 14, a polycondensation was performed under the same conditions and with the same additives as in Example 15, but without isophthalic acid. Along with the hydrotalcite Pural (20 g), 80 g Irganox 1425 (phosphoric acid ester-based stabilizer from Ciba Geigy) was added to the reaction mixture.

[0039] Table 3 contains characteristic values for individual granulate fractions.

EXAMPLE 17 (EXEMPLIFIED EMBODIMENT)

[0040] Analogous to Example 16, but with the quantity of isophthalic acid given in Example 14, 20 g Pural, and 20 g Irganox 1425.

[0041] Characteristic values of the granulate fractions are contained in Table 3.

EXAMPLE 18 (EXEMPLIFIED EMBODIMENT)

[0042] Analogous to Example 17, but with 20 g Pural and 40 g Irganox 1425.

[0043] The characteristic values determined for individual product fractions are summarized in Table 3.

EXAMPLE 19 (COMPARISON EXAMPLE)

[0044] Analogous to Example 17, but with 20 g Pural and 40 g Irgafos 168.

[0045] Characteristic values of the granulate fractions are contained in Table 3

EXAMPLE 20 (EXEMPLIFIED EMBODIMENT)

[0046] Analogous to Example 17, but with 20 g Pural and 40 g Irganox PEPQ. TABLE 3 Characteristic values of various polyester fractions as a function of the catalyst-stabilizer system used. Product Catalyst Stabilizer Intrinsic fraction concentration concentration viscosity B* - color a - color Experiment no. Catalyst (ppm) Stabilizer (ppm) (dl/g) a-IV (dl/g) number number Example 14 1 Antimony 640 0.69 0.035 1.08 1.12 (comparison 4 triacetate 0.655 3.2 example) Example 15 1 Hydrotalcite 250 0.7051 0.093 0.53 4.82 (comparison 4 0.6113 5.35 example) Example 16 1 Hydrotalcite 250 Irganox 1000 0.6463 0.021 −4.61 2.5 (exemplified 6 1425 0.6251 −2.11 embodiment) Example 17 1 Hydrotalcite 250 Irganox 250 0.674 0.068 −0.31 3.73 (exemplified 5 1425 0.606 3.42 embodiment) Example 18 1 Hydrotalcite 250 Irganox 500 0.683 0.046 −2.54 3.2 (exemplified 5 1425 0.637 0.66 embodiment) Example 19 1 Hydrotalcite 250 Irgafos 500 0.6848 0.073 1.98 1.83 (comparison 5 168 0.6118 3.81 example*) Example 20 1 Hydrotalcite 250 Irganox 500 0.672 0.048 −2.32 3.03 (exemplified 5 PEPQ 0.624 0.71 embodiment)

[0047] Tables 2 and 3 illustrate the advantages of hydrotalcites as catalysts for polycondensation reactions. Hydrotalcites at substantially lower concentrations have the same catalytic effectiveness as conventional polycondensation catalysts such as antimony compounds. In combination with the excellent food compatibility, with this new class of polycondensation catalysts an excellent alternative is provided to the currently commercially utilized catalytically active compounds.

[0048] The combination hydrotalcite/phosphoric acid ester or phosphorous acid ester permits the synthesis of polyesters with a very high thermal stability. The molecular weight breakdown during processing listed in Table 3 is more favorable than in the case of the polyesters produced under antimony catalysis.

[0049] In addition, the products are characterized by a low color tint.

[0050] The combination hydrotalcite/phosphoric acid ester or phosphorous acid ester can also used for the synthesis of other polyesters and for insertion of other monomers into polyalkylene terephthalate 

1. Catalyst systems for polycondensation reactions, characterized in that they are untreated or calcinated hydrotalcite-analogous derivatives of the general formula [M(II)_(1−x)M(III)_(x)(OH)₂]^(x+)(A^(n−) _(x/n)).mH₂O wherein M(II): divalent metals, M(III): trivalent metals, and A: anions, alone or in combination with phosphorus compounds that contain at least one hydrolyzable phosphorus-oxygen bond.
 2. Catalyst systems for polycondensation reactions in accordance with claim 1, characterized in that M(II) is Mg or Zn or Ni or Cu or Fe(II) or Co.
 3. Catalyst systems for polycondensation reactions according to claims 1 or 2, characterized in that M(III) is Al or Fe(III).
 4. Catalyst systems for polycondensation reactions according to any of claims 1 to 3, characterized in that A are carbonates, titanyls or borates.
 5. Catalyst systems for polycondensation reactions according to any of claims 1 to 4, characterized in that the calcination of the hydrotalcite-analogous compounds is carried out at temperatures of 200° C. to 800° C., preferably at 400° C. to 650° C.
 6. Catalyst systems for polycondensation reactions in accordance with any of claims 1 to 5, characterized in that the polycondensation is carried out with the catalysts under vacuum in liquid phase at temperatures of 230° C. to 280° C. and in solid phase at temperatures of 170 to 240° C.
 7. Catalyst systems for polycondensation reactions in accordance with any of claims 1 through 6, characterized in that the particle sizes of the hydrotalcites used are in the range of 0.1 to 50 μm, preferably 0.5 to 5 μm.
 8. Catalyst systems for polycondensation reactions in accordance with claim 1, characterized in that as the phosphorus compounds, phosphoric acid esters or esters of phosphorous acid are used.
 9. Catalyst systems for polycondensation reactions in accordance with claim 8, characterized in that the catalyst system is used in the proportion, hydrotalcite to phosphorus compound, of 1:0.5 to 1:4, preferably of 1:1 to 1:2.
 10. A polycondensation product made using a catalyst as described in any of claims 1 through 9 characterized in that the product is substantially free of heavy metals.
 11. A polycondensation product as in claim 10 further characterized in that the product is suitable for use in bottles, sheets, films or fibers. 